Let's roll up our sleeves and solve this. We have 660 and we're going to multiply it by 9, essentially adding 660 to itself 9 times.
Step 1: 0 + 660 = 660
Step 2: 660 + 660 = 1320
Step 3: 1320 + 660 = 1980
Step 4: 1980 + 660 = 2640
Step 5: 2640 + 660 = 3300
Step 6: 3300 + 660 = 3960
Step 7: 3960 + 660 = 4620
Step 8: 4620 + 660 = 5280
Step 9: 5280 + 660 = 5940

So, 660*9 = 5940